Flexible tubular pipes for transporting fluids usually associated with the oil and gas industry have been used for many years. Bonded flexible pipes of these types have traditionally employed an external sheath formed by thermoset elastomers, polyethylene, or nylon.
However, although these materials provide excellent flexibility, they have disadvantages. For example the thermoset elastomers have higher production cost and production of long lengths is more difficult. Also, the polyethylene sheaths becomes stiff at low temperature, have limited fatigue resistance, and a relatively high thermal conductivity. Moreover, nylon becomes stiff and tends to be brittle at arctic temperatures and, in addition, is susceptible to degradation in the presence of moisture at elevated temperatures and therefore must be dried thoroughly prior to extrusion processing.
In view of the above there is a trend towards forming the outer sheaths of flexible pipes with a polymeric material that has resistance to fatigue in dynamic situations. For example, certain grades of polyamide 11 are routinely used (such as products sold by Atofina under the trade name RILSAN). Although this material gives excellent results, it is a high cost material and cannot be used in some cases because of its limited resistance to high temperatures and its sensitivity to the presence of water.
Therefore there is a need for a flexible tubular pipe having an impervious outer sheath that eliminates the above disadvantages.